Wednesday, June 30, 2010

Evidence for a recoiling black hole has been found using data from the Chandra X-ray Observatory, XMM-Newton, the Hubble Space Telescope (HST), and several ground-based telescopes. This black hole kickback was caused either by a slingshot effect produced in a triple black hole system, or from the effects of gravitational waves produced after two supermassive black holes merged a few million years earlier.

The discovery of this object, located in this composite image, comes from a large, multi-wavelength survey, known as the Cosmic Evolution Survey (COSMOS). This survey includes data from Chandra, HST, XMM- Newton, as well as ground-based observatories. Of the 2,600 X-ray sources found in COSMOS, only one -- named CID-42 and located in a galaxy about 3.9 billion light years away -- coincides with two very close, compact optical sources (The two sources are seen in the HST data, but they are too close for Chandra to resolve separately.) In this image, the X-ray source detected by Chandra is colored blue, while the Hubble data are seen in gold.

The galaxy's long tail suggests that a merger between galaxies has occurred relatively recently, only a few million years earlier. Data from the Very Large Telescope and the Magellan telescope give evidence that the difference in speed of the two optical sources is at least three million miles an hour.

The X-ray spectra from Chandra and XMM-Newton provide extra information about CID-42. Absorption from iron-rich gas shows that gas is moving rapidly away from us in the rest frame of the galaxy. This could be gas in the galaxy between us and one of the black holes that is falling into the black hole, or it could be gas on the far side of the black hole that is blowing away.

Taken together, these pieces of information allow for two different scenarios for what is happening in this system. In the first scenario, the researchers surmise that a triple black hole encounter was produced by a two-step process. First, a collision between two galaxies created a galaxy with a pair of black holes in a close orbit. Before these black holes could merge, another galaxy collision occurred, and another supermassive black hole spiraled toward the existing black hole pair.

The interaction among the three black holes resulted in the lightest one being ejected. In this case, the optical source in the lower left of the image is an active galactic nucleus (AGN) powered by material being pulled along by, and falling onto, the escaping supermassive black hole. The source in the upper right is an AGN containing the black hole that resulted from a merger between the two remaining black holes.

In this slingshot scenario, the high-speed X-ray absorption can be explained as a high-speed wind blowing away from the AGN in the upper right that absorbs light from the AGN in the lower left. Based on its optical spectrum, the AGN in the upper right is thought to be obscured by a torus of dust and gas. In nearly all cases a wind from such an AGN would be undetectable, but here it is illuminated by the other AGN, giving the first evidence that fast winds exist in obscured AGN.

An alternative explanation posits a merger between two supermassive black holes in the center of the galaxy. The asymmetry of the gravitational waves emitted in this process caused the merged black hole to be kicked away from the center of the galaxy. In this scenario, the ejected black hole is the point source in the lower left and a cluster of stars left behind in the center of the galaxy is in the upper right. The observed X-ray absorption would be caused by gas falling onto the recoiling black hole.

Future observations may help eliminate or further support one of these scenarios. A team of researchers led by Francesca Civano and Martin Elvis of the Harvard-Smithsonian Center for Astrophysics (CfA) will publish their work on CID-42 in the July 1st edition of The Astrophysical Journal.

The second scenario, concerning the recoil of a supermassive black hole caused by a gravitational wave kick, has recently been proposed by Peter Jonker from the Netherlands Institute for Space Research in Utrecht as a possible explanation for a source in a different galaxy. In this study, led by Peter Jonker from the Netherlands Institute for Space Research in Utrecht, a Chandra X-ray source was discovered about ten thousand light years, in projection, away from the center of a galaxy. Three possible explanations for this object are that it is an unusual type of supernova, or an ultraluminous X- ray source with a very bright optical counterpart or a recoiling supermassive black hole resulting from a gravitational wave kick.

An international team unveiled the origin of the giant gas ring in the Leo group of galaxies. With the Canada-France-Hawaii Telescope, the scientists were able to detect an optical signature of the ring corresponding to star forming regions. This observation rules out the primordial nature of the gas, which is of galactic origin. Thanks to numerical simulations made at CEA, a scenario for the formation of this ring has been proposed: a violent collision between two galaxies, slightly more than one billion years ago. The results will be published in the Astrophysical Journal Letters.

In the current theories on galaxy formation, the accretion of cold primordial gas is a key-process in the early steps of galaxy growth. This primordial gas is characterized by two main features: it has never sojourned in any galaxy and it does not satisfy the conditions required to form stars. Is such an accretion process still ongoing in nearby galaxies? To answer the question, large sky surveys are undertaken attempting to detect the primordial gas.

The Leo ring, a giant ring of cold gas 650,000 light-years wide surrounding the galaxies of the Leo group, is one of the most dramatic and mysterious clouds of intergalactic gas. Since its discovery in the 80s, its origin and its nature were debated. Last year, studies of the metal abundances in the gas led to the belief that the ring was made of this famous primordial gas.

Thanks to the sensitivity of the Canada-France-Hawaii Telescope MegaCam camera, the international team observed for the first time the optical counterpart of the densest regions of the ring, in visible light instead of radio waves. Emitted by massive young stars, this light points to the fact that the ring gas is able to form stars.

A ring of gas and stars surrounding a galaxy immediately suggests another kind of ring: a so-called collisional ring, formed when two galaxies collide. Such a ring is seen in the famous Cartwheel galaxy. Would the Leo ring be a collisional ring too?

In order to secure this hypothesis, the team used numerical simulations (performed on supercomputers at CEA) to demonstrate that the ring was indeed the result of a giant collision between two galaxies more than 38 million light-years apart: at the time of the collision, the disk of gas of one of the galaxies is blown away and will eventually form a ring outside of the galaxy. The simulations allowed the identification of the two galaxies which collided: NGC 3384, one of the galaxies at the center of the Leo group, and M96, a massive spiral galaxy at the periphery of the group. They also gave the date of the collision: more than a billion years ago!

The gas in the Leo ring is definitely not primordial. The hunt for primordial gas is still open!

Ancient stars 2 – Simulation showing the stellar halo around the Milky Way in the present day. Credit: Andrew Cooper / Durham University

Many of the Milky Way’s ancient stars are remnants of other smaller galaxies torn apart by violent galactic collisions around five billion years ago, according to researchers at Durham University, who publish their results in a new paper in the journal Monthly Notices of the Royal Astronomical Society.

Scientists at Durham’s Institute for Computational Cosmology and their collaborators at the Max Planck Institute for Astrophysics, in Germany, and Groningen University, in Holland, ran huge computer simulations to recreate the beginnings of our Galaxy.

The simulations revealed that the ancient stars, found in a stellar halo of debris surrounding the Milky Way, had been ripped from smaller galaxies by the gravitational forces generated by colliding galaxies.

Cosmologists predict that the early Universe was full of small galaxies which led short and violent lives. These galaxies collided with each other leaving behind debris which eventually settled into more familiar looking galaxies like the Milky Way.

The researchers say their finding supports the theory that many of the Milky Way’s ancient stars had once belonged to other galaxies instead of being the earliest stars born inside the Galaxy when it began to form about 10 billion years ago.

Lead author Andrew Cooper, from Durham University’s Institute for Computational Cosmology, said: “Effectively we became galactic archaeologists, hunting out the likely sites where ancient stars could be scattered around the galaxy.

“Our simulations show how different relics in the Galaxy today, like these ancient stars, are related to events in the distant past.

“Like ancient rock strata that reveal the history of Earth, the stellar halo preserves a record of a dramatic primeval period in the life of the Milky Way which ended long before the Sun was born.”

The computer simulations started from shortly after the Big Bang, around 13 billion years ago, and used the universal laws of physics to simulate the evolution of dark matter and the stars.

These simulations are the most realistic to date, capable of zooming into the very fine detail of the stellar halo structure, including star “streams” – which are stars being pulled from the smaller galaxies by the gravity of the dark matter.

One in one hundred stars in the Milky Way belong to the stellar halo, which is much larger than the Galaxy’s familiar spiral disk. These stars are almost as old as the Universe.

“They show that vital clues to the early, violent history of the Milky Way lie on our galactic doorstep.

“Our data will help observers decode the trials and tribulations of our Galaxy in a similar way to how archaeologists work out how ancient Romans lived from the artefacts they left behind.”

The research is part of the Aquarius Project, which uses the largest supercomputer simulations to study the formation of galaxies like the Milky Way and was partly funded by the UK’s Science and Technology Facilities Council (STFC).

Aquarius was carried out by the Virgo Consortium, involving scientists from the Max Planck Institute for Astrophysics in Germany, the Institute for Computational Cosmology at Durham University, UK, the University of Victoria in Canada, the University of Groningen in the Netherlands, Caltech in the USA and Trieste in Italy.

Durham’s cosmologists will present their work to the public as part of the Royal Society's 350th anniversary 'See Further' exhibition, held at London's Southbank Centre until July 4th.

The highlight of their 'Cosmic Origins' exhibit is an award winning 3-D movie describing how the Milky Way formed. Visitors to the exhibit can also create their own star streams by colliding galaxies with an interactive 3-D simulation.

Durham University is a member of the 1994 Group of 19 leading research-intensive universities. The Group was established in 1994 to promote excellence in university research and teaching. Each member undertakes diverse and high-quality research, while ensuring excellent levels of teaching and student experience.www.1994group.ac.uk

The Royal Astronomical Society

The Royal Astronomical Society (RAS: www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3000 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

This magnificent view of the region around the star R Coronae Australis was created from images taken with the Wide Field Imager (WFI) at ESO’s La Silla Observatory in Chile. R Coronae Australis lies at the heart of a nearby star-forming region and is surrounded by a delicate bluish reflection nebula embedded in a huge dust cloud. The image reveals surprising new details in this dramatic area of sky.

The star R Coronae Australis lies in one of the nearest and most spectacular star-forming regions. This portrait was taken by the Wide Field Imager (WFI) on the MPG/ESO 2.2-metre telescope at the La Silla Observatory in Chile. The image is a combination of twelve separate pictures taken through red, green and blue filters.

This image shows a section of sky that spans roughly the width of the full Moon. This is equivalent to about four light-years at the distance of the nebula, which is located some 420 light-years away in the small constellation of Corona Australis (the Southern Crown). The complex is named after the star R Coronae Australis, which lies at the centre of the image. It is one of several stars in this region that belong to the class of very young stars that vary in brightness and are still surrounded by the clouds of gas and dust from which they formed.

The intense radiation given off by these hot young stars interacts with the gas surrounding them and is either reflected or re-emitted at a different wavelength. These complex processes, determined by the physics of the interstellar medium and the properties of the stars, are responsible for the magnificent colours of nebulae. The light blue nebulosity seen in this picture is mostly due to the reflection of starlight off small dust particles. The young stars in the R Coronae Australis complex are similar in mass to the Sun and do not emit enough ultraviolet light to ionise a substantial fraction of the surrounding hydrogen. This means that the cloud does not glow with the characteristic red colour seen in many star-forming regions.

The huge dust cloud in which the reflection nebula is embedded is here shown in impressively fine detail. The subtle colours and varied textures of the dust clouds make this image resemble an impressionist painting. A prominent dark lane crosses the image from the centre to the bottom left. Here the visible light emitted by the stars that are forming inside the cloud is completely absorbed by the dust. These objects could only be detected by observing at longer wavelengths, by using a camera that can detect infrared radiation.

R Coronae Australis itself is not visible to the unaided eye, but the tiny, tiara-shaped constellation in which it lies is easily spotted from dark sites due to its proximity on the sky to the larger constellation of Sagittarius and the rich star clouds towards the centre of our own galaxy, the Milky Way.

More information

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

Tuesday, June 29, 2010

The Hubble Space Telescope captured this beautiful image of NGC 6326, a planetary nebula with glowing wisps of outpouring gas that are lit up by a central star nearing the end of its life. When a star ages and the red giant phase of its life comes to an end, it starts to eject layers of gas from its surface leaving behind a hot and compact white dwarf. Sometimes this ejection results in elegantly symmetric patterns of glowing gas, but NGC 6326 is much less structured. This object is located in the constellation of Ara, the Altar, about 11 000 light-years from Earth.

Planetary nebulae are one of the main ways in which elements heavier than hydrogen and helium are dispersed into space after their creation in the hearts of stars. Eventually some of this outflung material may form new stars and planets. The vivid red and blue hues in this image come from the material glowing under the action of the fierce ultraviolet radiation from the still hot central star.

This picture was created from images taken using the Hubble Space Telescope’s Wide Field Planetary Camera 2. The red light was captured through a filter letting through the glow from hydrogen gas (F658N). The blue glow comes from ionised oxygen and was recorded through a green filter (F502N). The green layer of the image, which shows the stars well, was taken through a broader yellow filter (F555W). The total exposure times were 1400 s, 360 s and 260 s respectively. The field of view is about 30 arcseconds across.

Thursday, June 24, 2010

Pulsars appear to be able to switch between two states which differ in the current of charged particles flowing from the surface into outer space. This change in current results in a change of slow-down in their rotation rate, such that the pulsar 'brakes' faster (upper panel) when the currents are large and 'brakes' less fast when the currents are weak (lower panel). These currents also result in a change in the shape of the beam emitted by the pulsar, and hence in the shape of the pulse, or tick, as the beam crosses a radio telescope. These processes are illustrated in thismpeg simulation. Credit: Michael Kramer, University of Manchester.

The 76-metre Lovell Radio Telescope at Jodrell Bank Observatory

An international team of scientists have developed a promising new technique which could turn pulsars - superb natural cosmic clocks - into even more accurate time-keepers.

This important advance, led by scientists at The University of Manchester and appearing today (June 24th) in the journal Science Express, could improve the search for gravitational waves and help studies into the origins of the universe.

The direct discovery of gravitational waves, which pass over cosmic clocks and cause them to change, could allow scientists to study violent events such as the merging of super-massive black holes and help understand the universe shortly after its formation in the Big Bang.

The scientists made their breakthrough using decades-long observations from the 76-m Lovell radio telescope at The University of Manchester's Jodrell Bank Observatory to track the radio signals of extreme stars known as pulsars.

Pulsars are spinning collapsed stars which have been studied in great detail since their discovery in 1967. The extremely stable rotation of these cosmic fly-wheels has previously led to the discovery of the first planets orbiting other stars and provided stringent tests for theories of gravity that shape the Universe.

However, this rotational stability is not perfect and, until now, slight irregularities in their spin have significantly reduced their usefulness as precision tools.

The team, led by the University of Manchester's Professor Andrew Lyne, has used observations from the Lovell telescope to explain these variations and to demonstrate a method by which they may be corrected.

Professor Lyne explains:

"Mankind's best clocks all need corrections, perhaps for the effects of changing temperature, atmospheric pressure, humidity or local magnetic field. Here, we have found a potential means of correcting an astrophysical clock".

The rate at which all pulsars spin is known to be decreasing very slowly. What the team has found is that the deviations arise because there are actually two spin-down rates and not one, and that the pulsar switches between them, abruptly and rather unpredictably.

These changes are associated with a change in the shape of the pulse, or tick, emitted by the pulsar. Because of this, precision measurements of the pulse shape at any particular time indicate exactly what the slowdown rate is and allow the calculation of a "correction". This significantly improves their properties as clocks.

The results give a completely new insight into the extreme conditions near neutron stars and also offer the potential for improving already very precise experiments in gravitation.

It is hoped that this new understanding of pulsar spin-down will improve the chances that the fastest spinning pulsars will be used to make the first direct detection of ripples, known as gravitational waves, in the fabric of space-time.

The University of Manchester team worked closely on the project with Dr George Hobbs of the Australia Telescope National Facility, Professor Michael Kramer of the Max Planck Institute for Radioastronomy and Professor Ingrid Stairs of the University of British Columbia.

The research was funded by the Science and Technology Facilities Council. Their Director of Science, Professor John Womersley, said:

"Astronomy is unlike most other sciences, as we cannot go out and measure directly the properties of stars and galaxies.

They have to be calculated based on our understanding of how the Universe works - which means that something as significant as being able to use pulsars as cosmic clocks, a new standard for time measurement, will have far-reaching consequences for advancing science and our understanding of the Universe."

Many observatories around the world are attempting to use pulsars in order to detect the gravitational waves that are expected to be created by super-massive binary black holes in the Universe.

With the new technique, the scientists may be able to reveal the gravitational wave signals that are currently hidden because of the irregularities in the pulsar rotation.

Head of the Pulsar Group at The University of Manchester Dr Ben Stappers said:

"These exciting results were only possible because of the quality and duration of the unique Lovell Telescope pulsar timing database".

Notes for editors

Professor Andrew Lyne is available for interview or background information.

Images of the Lovell Telescope and of pulsars are available on request from the Press Office.

The paper: 'Switched Magnetospheric Regulation of Pulsar Spin-down', by Andrew Lyne, George Hobbs, Michael Kramer, Ingrid Stairs, Ben Stappers, is available on request and can also be found in the journal 'Science Express' and is available as a pdf downloadhere. Supplementary background material is availablehere.

Images of the Lovell Telescope are available on request from the Press Office.

Background Information

A pulsar is a neutron star, which is the collapsed core of a massive star that has ended its life in a supernova explosion. Weighing more than our Sun, yet only 20 kilometres across, and hence only the size of a city like Manchester, these incredibly dense cosmic fly-wheels produce beams of radio waves which sweep around the sky like a lighthouse, often hundreds of times a second. Radio telescopes receive a regular train of pulses as the beam repeatedly crosses the Earth so that the object is observed as a pulsating radio signal.

The clock-like nature of the arrival times of these pulses at the Earth means that pulsars have been used for some of the most precise studies of our understanding of the General Relativity theory of gravity. The best pulsars are the fastest rotating, called millisecond pulsars, which keep time to better than a millionth of a second over a year. These sources rotate up to 700 times a second and are currently being used to try and make the first ever detection of gravitational waves. This new insight provides an opportunity to achieve the necessary precision.

The Jodrell Bank work was supported by funding from the UK Science and Technology Facilities Council (STFC). Jodrell Bank Centre for Astrophysics is part of the School of Physics and Astronomy at The University of Manchester. Jodrell Bank is home to the Lovell Radio Telescope and the MERLIN/VLBI National Facility which is operated by the University on behalf of STFC.

STFC is the UK's strategic science investment agency. It fundsresearch, education and public understanding in four areas of science - particle physics, astronomy, cosmology and space science. STFC is government funded and provides research grants and studentships to scientists in British universities, gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Laboratory for Particle Physics (CERN), and the European Space Agency. It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, the UK Astronomy Technology Centre at the Royal Observatory, Edinburgh and the MERLIN/VLBI National Facility, which includes the Lovell Telescope at Jodrell Bank observatory.

This artist's concept shows simulated data predicting the hundreds of failed stars, or brown dwarfs, that NASA's Wide-field Infrared Survey Explorer (WISE) is expected to add to the population of known stars in our solar neighborhood. Image credit: AMNH/UCB/NASA/JPL-Caltech.Full image and caption

This image shows what astronomers think is one of the coldest brown dwarfs discovered so far (red dot in middle of frame).Full image and caption

Astronomers have uncovered what appear to be 14 of the coldest stars known in our universe. These failed stars, called brown dwarfs, are so cold and faint that they'd be impossible to see with current visible-light telescopes. Spitzer's infrared vision was able to pick out their feeble glow, much as a firefighter uses infrared goggles to find hot spots buried underneath a dark forest floor.

The brown dwarfs join only a handful of similar objects previously discovered. The new objects are between the temperatures of about 450 Kelvin to 600 Kelvin (350 to 620 degrees Fahrenheit). As far as stars go, this is bitter cold -- as cold, in some cases, as planets around other stars.

These cool orbs have remained elusive for years, but will soon start coming out of the dark in droves. NASA's Wide-field Infrared Survey Explorer (WISE) mission, which is up scanning the entire sky now in infrared wavelengths, is expected to find hundreds of objects of a similarly chilly disposition, if not even colder. WISE is searching a volume of space 40 times larger than that sampled in the recent Spitzer study, which concentrated on a region in the constellation Boötes. The Spitzer mission is designed to look at targeted patches of sky in detail, while WISE is combing the whole sky.

"WISE is looking everywhere, so the coolest brown dwarfs are going to pop up all around us," said Peter Eisenhardt, the WISE project scientist at NASA's Jet Propulsion Laboratory, Pasadena, Calif., and lead author of a recent paper in the Astronomical Journal on the Spitzer discoveries. "We might even find a cool brown dwarf that is closer to us than Proxima Centauri, the closest known star."

Brown dwarfs form like stars out of collapsing balls of gas and dust, but they are puny in comparison, never collecting enough mass to ignite nuclear fusion and shine with starlight. The smallest known brown dwarfs are about 5 to 10 times the mass of our planet Jupiter -- that's as massive as some known gas-giant planets around other stars. Brown dwarfs start out with a bit of internal heat left over from their formation, but with age, they cool down. The first confirmed brown dwarf was announced in 1995.

"Brown dwarfs are like planets in some ways, but they are in isolation," said astronomer Daniel Stern, co-author of the Spitzer paper at JPL. "This makes them exciting for astronomers -- they are the perfect laboratories to study bodies with planetary masses."

Most of the new brown dwarfs found by Spitzer are thought to belong to the coolest known class of brown dwarfs, called T dwarfs, which are defined as being less than about 1,500 Kelvin (2,240 degrees Fahrenheit). One of the objects appears to be so cold that it may even be a long-sought Y dwarf -- a proposed class of even colder stars. The T and Y classes are part of a larger system categorizing all stars; for example, the hottest, most massive stars are O stars; our sun is a G star.

"Models indicate there may be an entirely new class of stars out there, the Y dwarfs, that we haven't found yet," said co-author Davy Kirkpatrick, a co-author of the study and a member of the WISE science team at the California Institute of Technology, Pasadena, Calif. "If these elusive objects do exist, WISE will find them." Kirkpatrick is a world expert in brown dwarfs -- he came up with L, T and Y classifications for the cooler stars.

Kirkpatrick says that it's possible that WISE could find an icy, Neptune-sized or bigger object in the far reaches of our solar system -- thousands of times farther from the sun than Earth. There is some speculation amongst scientists that such a cool body, if it exists, could be a brown dwarf companion to our sun. This hypothetical object has been nicknamed "Nemesis."

"We are now calling the hypothetical brown dwarf Tyche instead, after the benevolent counterpart to Nemesis," said Kirkpatrick. "Although there is only limited evidence to suggest a large body in a wide, stable orbit around the sun, WISE should be able to find it, or rule it out altogether."

The 14 objects found by Spitzer are hundreds of light-years away -- too far away and faint for ground-based telescopes to see and confirm with a method called spectroscopy. But their presence implies that there are a hundred or more within only 25 light-years of our sun. Because WISE is looking everywhere, it will find these missing orbs, which will be close enough to confirm with spectroscopy. It's possible that WISE will even find more brown dwarfs within 25-light years of the sun than the number of stars known to exist in this space.

"WISE is going to transform our view of the solar neighborhood," said Eisenhardt. We'll be studying these new neighbors in minute detail -- they may contain the nearest planetary system to our own."

Other authors of the Spitzer paper are Roger Griffith and Amy Mainzer of JPL; Ned Wright, A.M. Ghez and Quinn Konopacky of UCLA; Matthew Ashby and Mark Brodwin of the Harvard-Smithsonian Center for Astrophysics, Cambridge; Mass., Michael Brown of Monash University, Australia; R.S. Bussmann of the University of Arizona, Tucson; Arjun Dey of National Optical Astronomy Observatory, Tucson, Ariz.; Eilat Glikman of Caltech; Anthony Gonzalez and David Vollbach of the University of Florida, Gainesville; and Shelley Wright of the University of California, Berkeley.

JPL manages the Wide-field Infrared Survey Explorer for NASA's Science Mission Directorate, Washington. The principal investigator, Edward Wright, is at UCLA. The mission was competitively selected under NASA's Explorers Program managed by the Goddard Space Flight Center, Greenbelt, Md. The science instrument was built by the Space Dynamics Laboratory, Logan, Utah, and the spacecraft was built by Ball Aerospace & Technologies Corp., Boulder, Colo. Science operations and data processing take place at the Infrared Processing and Analysis Center at the California Institute of Technology in Pasadena. Caltech manages JPL for NASA.

1. An artist’s impression of the black hole (in the centre), surrounding disk of hot material (depicted in white, green and blue) and outer torus (in red) that make up the central region of the quasar SDSS J0123+01. The outer radius of the torus is about 100 light years across. If we see the torus edge on (as in the image) the bright emission from the central hot disk is blocked and the system is categorised as a type 2 quasar. Credit: NASA/CXC/M.Weiss

2. An image of the field around the type 2 quasar SDSS J0123+01 obtained with the OSIRIS tuneable filter on GTC. The red colour shows regions where light is emitted mainly by stars. The green colour shows emission from hot ionized gas. Yellow indicates a mixture of both. The image reveals the existence of a giant nebula of ionized gas which extends for 180 kiloparsecs (590000 light years) or 6 times the size of our galaxy, the Milky Way. The nebula encompasses a bridge of material that connects the quasar physically with the neighbouring galaxy it is interacting with. Credit: Montserrat Villar Martin (IAA-CSIC)

View an animated artistic impression of quasar with accreation disk and jet

Using two of the world’s largest telescopes, an international team of astronomers have found evidence of a collision between galaxies driving intense activity in a highly luminous quasar. The scientists, led by Montserrat Villar Martin of the Instituto de Astrofisica de Andalucía-CSIC in Spain, used the Very Large Telescope (VLT) in Chile and the Gran Telescopio Canarias (GTC) on La Palma in the Canary Islands, to study activity from the quasar SDSS J0123+00. They publish their work in a paper in the journal Monthly Notices of the Royal Astronomical Society.

Several types of galaxies, known as active galaxies, emit enormous amounts of energy from their central region or nucleus, with the most luminous objects known as quasars. Most scientists argue that quasars contain a central black hole, with a mass of at least several million Suns.

The intense gravitational field created by the black hole drags material inexorably inwards. Before falling in, this material settles in an accretion disk where it becomes very hot and emits large amounts of energy responsible for most of the brightness of the quasar. Around the central quasar ‘engine’ is a torus (thick ring) opaque to the visible light emitted by the accretion disk. From a terrestrial perspective, if the torus is face-on then the radiation from the disk can be seen and the system is designated type 1, whereas in type 2 quasars the torus is edge-on and the radiation is concealed.

“Type 2 quasars are a family of still rather unknown galaxies”, explains Montserrat Villar-Martin, who led the research team, “which so far have been investigated mostly from a statistical point of view.

“The goal of our work is to study their individual characteristics in detail. In our study we have obtained some surprising results. For example, we have observed a giant nebula of ionized gas associated with SDSS J0123+00, and signs of an interaction with a nearby galaxy.

“This strengthens the idea that activity in galaxies is partly driven by the exchange of material between the active galaxies (or quasars) and their neighbours”.

Although type 2 quasars are more difficult to detect, they are unique laboratories that let astronomers study the quasar environment in great detail, thanks to the dimming of the central radiation by the surrounding torus.

In the case of SDSS J0123+00, one of the most important results is the discovery of an extended, faint nebula of ionized gas around the entire galaxy. The nebula is about six times larger than our own Milky Way Galaxy and, according to the authors, is probably made of the debris of the interaction between SDSS J0123+00 and its neighbour.

Part of the giant nebula is a bridge of material that connects the two galaxies. This strengthens the hypothesis that the quasar activity is triggered by the interaction between them, producing the accumulation of gas in the galactic central regions and providing material to feed the black hole. This process can also trigger the rapid formation of new stars.

The new results are the first based on images obtained with the tuneable filter of the Optical System for Imaging and low Resolution Integrated Spectroscopy (OSIRIS), the instrument installed on the GTC. The OSIRIS tuneable filter allows astronomers to observe objects in narrow windows across the spectrum of visible light from red to blue, something that with older systems would need more than five thousand narrow band filters.

The Royal Astronomical Society (RAS:www.ras.org.uk), founded in 1820, encourages and promotes the study of astronomy, solar-system science, geophysics and closely related branches of science. The RAS organizes scientific meetings, publishes international research and review journals, recognizes outstanding achievements by the award of medals and prizes, maintains an extensive library, supports education through grants and outreach activities and represents UK astronomy nationally and internationally. Its more than 3500 members (Fellows), a third based overseas, include scientific researchers in universities, observatories and laboratories as well as historians of astronomy and others.

Image caption: Illustration of radio observations of the galaxy IC 2497 with the European VLBI Network (EVN) and the UK's Multi-Element Radio Linked Interferometer Network MERLIN. The background image is an optical image of Hanny's Voorwerp and the neighbouring giant galaxy, IC 2497 (Credit: William Keel, Anna Manning, 3.5-m WIYN Telescope), while the magnification glass highlights the associated high-resolution radio observations. Two very compact sources are detected at the heart of IC2497 with the EVN, signalling the presence of an active galactic nucleus there, i.e. an accreting super massive black hole. The surrounding smooth and extended radio emission, arises from a so-called "nuclear starburst" - as the name suggests, this implies that a huge burst of star formation is going on within the central regions of IC 2497. (Copyright: ASTRON).

A group of researchers, led by Professor Michael Garrett, General Director of the Netherlands Institute for Radio Astronomy, ASTRON, have made new, high resolution radio observations of the region of space around Hanny's Voorwerp, the mysterious, greenish gas cloud discovered by Dutch school teacher Hanny van Arkel.

The astronomers undertook an observational campaign at radio wavelengths using the European Very Long Baseline Interferometry Network (EVN) and the UK's Multi-Element Radio Linked Interferometer Network (MERLIN), pointing their telescopes at the centre of the neighbouring galaxy IC 2497. In these measurements, several radio telescopes across Europe and the UK were linked together in real-time, in order to gain a detailed picture of the very central region of the galaxy. They observed a field a few arcseconds (the 3600th part of a degree) across, with a spatial resolution of about 70 milliarcseconds (0.07 arcseconds).

According to Garrett: "the observations show two bright and very compact sources with broadband spectra that argue strongly for the existence of an active galactic nucleus (AGN) at the centre of the galaxy, IC2497. One of the sources appears to be identified with the base of the super-massive blackhole at the centre of the AGN itself, while the other one is likely to be the result of an energetic jet expelled by the black-hole and now interacting with the dense gas that surrounds IC2497". The radiation output from the AGN is believed to heat Hanny's Voorwerp to a temperature above 10000 degrees.

But this is only part of the story. It also appears that surrounding the AGN, a lot of extended radio emission is also observed. The researchers argue that this is radio emission associated with a nuclear starburst. "We knew that IC 2497 is forming stars, but we were susprised to find that the star formation seems to be concentrated in a very small central region, only 3000 light years across", Hayden Rampadarath (University of Machester) explains. Garrett: "It is fairly unusual to find both vigorous star formation and AGN radio activity in the same system and on similar scales. It seems that IC2497 swings both ways".

The radio observations show that in this small region, IC 2497 is producing stars with a total mass of 70 suns every year. This star formation rate is pretty large, especially in the local Universe - it is about 6 times higher than in the nearby 'Starburst-Galaxy' poster-child, M82." "We know of only a few hundred of these types of galaxy, Luminous Infrared Galaxies, LIRGs, in the local universe", Gyula Józsa, support scientist at ASTRON, adds, "but they must have been much more frequent in the past". At half the universe's age, most stars have been formed in LIRGs. It is also typical that for this kind of galaxy large amounts of dust obscure optical and ultraviolet light towards the observer.

The observations support the group's earlier hypothesis that a hidden AGN in the centre of IC2497 is ionising a distinct region of gas that surrounds the giant galaxy. That distinct region is what we know as Hanny's Voorwerp. Such phenomenae must be rare in the local Universe, as they depend on a specific geometry of the observer, galaxy and gas, plus the interaction of several galaxies in the field in order to fuel the AGN and the starburst, and to create the gas reservoir that forms part of the Voorwerp.

Wednesday, June 23, 2010

Astronomers have measured a superstorm for the first time in the atmosphere of an exoplanet, the well-studied “hot Jupiter” HD209458b. The very high-precision observations of carbon monoxide gas show that it is streaming at enormous speed from the extremely hot day side to the cooler night side of the planet. The observations also allow another exciting “first” — measuring the orbital speed of the exoplanet itself, providing a direct determination of its mass.

The results appear this week in the journal Nature.

“HD209458b is definitely not a place for the faint-hearted. By studying the poisonous carbon monoxide gas with great accuracy we found evidence for a super wind, blowing at a speed of 5000 to 10 000 km per hour‚” says Ignas Snellen, who led the team of astronomers.

HD209458b is an exoplanet of about 60% the mass of Jupiter orbiting a solar-like star located 150 light-years from Earth towards the constellation of Pegasus (the Winged Horse). Circling at a distance of only one twentieth the Sun–Earth distance, the planet is heated intensely by its parent star, and has a surface temperature of about 1000 degrees Celsius on the hot side. But as the planet always has the same side to its star, one side is very hot, while the other is much cooler. “On Earth, big temperature differences inevitably lead to fierce winds, and as our new measurements reveal, the situation is no different on HD209458b,” says team member Simon Albrecht.

HD209458b was the first exoplanet to be found transiting: every 3.5 days the planet moves in front of its host star, blocking a small portion of the starlight during a three-hour period. During such an event a tiny fraction of the starlight filters through the planet’s atmosphere, leaving an imprint. A team of astronomers from the Leiden University, the Netherlands Institute for Space Research (SRON), and MIT in the United States, have used ESO’s Very Large Telescope and its powerful CRIRES spectrograph to detect and analyse these faint fingerprints, observing the planet for about five hours, as it passed in front of its star. “CRIRES is the only instrument in the world that can deliver spectra that are sharp enough to determine the position of the carbon monoxide lines at a precision of 1 part in 100 000,” says another team member Remco de Kok. “This high precision allows us to measure the velocity of the carbon monoxide gas for the first time using the Doppler effect.”

The astronomers achieved several other firsts. They directly measured the velocity of the exoplanet as it orbits its home star. “In general, the mass of an exoplanet is determined by measuring the wobble of the star and assuming a mass for the star, according to theory. Here, we have been able to measure the motion of the planet as well, and thus determine both the mass of the star and of the planet,” says co-author Ernst de Mooij.

Also for the first time, the astronomers measured how much carbon is present in the atmosphere of this planet. “It seems that H209458b is actually as carbon-rich as Jupiter and Saturn. This could indicate that it was formed in the same way,” says Snellen. “In the future, astronomers may be able to use this type of observation to study the atmospheres of Earth-like planets, to determine whether life also exists elsewhere in the Universe.”

More information

This research was presented in a paper that appears this week in the journal Nature: “The orbital motion, absolute mass, and high-altitude winds of exoplanet HD209458b”, by I. Snellen et al.

The team is composed of Ignas A. G. Snellen and Ernst J. W. de Mooij, (Leiden Observatory, The Netherlands), Remco J. de Kok (SRON, Utrecht, The Netherlands), and Simon Albrecht (Massachusetts Institute of Technology, USA).

ESO, the European Southern Observatory, is the foremost intergovernmental astronomy organisation in Europe and the world’s most productive astronomical observatory. It is supported by 14 countries: Austria, Belgium, the Czech Republic, Denmark, France, Finland, Germany, Italy, the Netherlands, Portugal, Spain, Sweden, Switzerland and the United Kingdom. ESO carries out an ambitious programme focused on the design, construction and operation of powerful ground-based observing facilities enabling astronomers to make important scientific discoveries. ESO also plays a leading role in promoting and organising cooperation in astronomical research. ESO operates three unique world-class observing sites in Chile: La Silla, Paranal and Chajnantor. At Paranal, ESO operates the Very Large Telescope, the world’s most advanced visible-light astronomical observatory and VISTA, the world’s largest survey telescope. ESO is the European partner of a revolutionary astronomical telescope ALMA, the largest astronomical project in existence. ESO is currently planning a 42-metre European Extremely Large optical/near-infrared Telescope, the E-ELT, which will become “the world’s biggest eye on the sky”.

A spectacular new NASA/ESA Hubble Space Telescope image — one of the largest ever released of a star-forming region — highlights N11, part of a complex network of gas clouds and star clusters within our neighbouring galaxy, the Large Magellanic Cloud. This region of energetic star formation is one of the most active in the nearby Universe.

The Large Magellanic Cloud contains many bright bubbles of glowing gas. One of the largest and most spectacular has the name LHA 120-N 11, from its listing in a catalogue compiled by the American astronomer and astronaut Karl Henize in 1956, and is informally known as N11. Close up, the billowing pink clouds of glowing gas make N11 resemble a puffy swirl of fairground candy floss. From further away, its distinctive overall shape led some observers to nickname it the Bean Nebula. The dramatic and colourful features visible in the nebula are the telltale signs of star formation. N11 is a well-studied region that extends over 1000 light-years. It is the second largest star-forming region within the Large Magellanic Cloud and has produced some of the most massive stars known.

It is the process of star formation that gives N11 its distinctive look. Three successive generations of stars, each of which formed further away from the centre of the nebula than the last, have created shells of gas and dust. These shells were blown away from the newborn stars in the turmoil of their energetic birth and early life, creating the ring shapes so prominent in this image.

Beans are not the only terrestrial shapes to be found in this spectacular high resolution image from the NASA/ESA Hubble Space Telescope. In the upper left is the red bloom of nebula LHA 120-N 11A. Its rose-like petals of gas and dust are illuminated from within, thanks to the radiation from the massive hot stars at its centre. N11A is relatively compact and dense and is the site of the most recent burst of star development in the region.

Other star clusters abound in N11, including NGC 1761 at the bottom of the image, which is a group of massive hot young stars busily pouring intense ultraviolet radiation out into space. Although it is much smaller than our own galaxy, the Large Magellanic Cloud is a very vigorous region of star formation. Studying these stellar nurseries helps astronomers understand a lot more about how stars are born and their ultimate development and lifespan.

Both the Large Magellanic Cloud and its small companion, the Small Magellanic Cloud, are easily seen with the unaided eye and have always been familiar to people living in the southern hemisphere. The credit for bringing these galaxies to the attention of Europeans is usually given to Portuguese explorer Fernando de Magellan and his crew, who viewed it on their 1519 sea voyage. However, the Persian astronomer Abd Al-Rahman Al Sufi and the Italian explorer Amerigo Vespucci recorded the Large Magellanic Cloud in 964 and 1503 respectively.

Notes

The Hubble Space Telescope is a project of international cooperation between ESA and NASA.